A simple and accurate micromethod for the determination of cell osmotic fragility is introduced. The method uses the Poiseuille's parabolic flow pattern together with the gravity to retain cells in a long capillary tube while a solution with decreasing osmolarity is passed through the tube for hemolysis. Hemoglobin released from the cells is quickly removed by the axial flow pattern and monitored with a spectrophotometer for recording the hemolysis curve. A comparison is made with present methods and test results from normal and abnormal individuals are reported. Advantages are simplicity, reproducibility, and accuracy with 1 to 2 ul sample doses and versatility for possible automation in clinical laboratory as well as a research tool for various types of cell studies.